Molding die set

ABSTRACT

A molding die set includes a first molding die which comprises cavities and a parting surface; a second molding die which comprises cavities and a parting surface arranged to face the first molding die; and an O-ring supported on the first molding die to surround the cavities and to have a peripheral line which does not extend outwardly from the parting surface.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority of Application No. H11-315311,filed Nov. 5, 1999 in Japan, the subject matter of which is incorporatedherein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a molding die set used for fabricatinga semiconductor apparatus, and to a method for fabricating asemiconductor apparatus using such a molding die set.

BACKGROUND OF THE INVENTION

According to a conventional technology, surface voids and/or inner voidsmay be made in a semiconductor package when a semiconductor apparatus,such as IC and LSI, is resin-molded using a thermosetting resin. Thusmolded package is treated as defective. In order to prevent voids in asemiconductor package, a mold chase unit is designed to be able toreduce the pressure therein.

OBJECTS OF THE INVENTION

Accordingly, an object of the present invention is to provide a moldingdie set whereby a molding process can be carried out at a desirablepressure-reduced condition in cavities.

Another object of the present invention is to provide a semiconductordevice package which is fabricated to reduce voids generated in a moldedpackage.

Additional objects, advantages and novel features of the presentinvention will be set forth in part in the description that follows, andin part will become apparent to those skilled in the art uponexamination of the following or may be learned by practice of theinvention. The objects and advantages of the invention may be realizedand attained by means of the instrumentalities and combinationsparticularly pointed out in the appended claims.

SUMMARY OF THE INVENTION

(1) First Aspect of the Present Invention

According to a first aspect of the present invention, a molding die setincludes a first molding die which comprises cavities and a partingsurface; a second molding die which comprises cavities and a partingsurface arranged to face the first molding die; and an O-ring supportedon the first molding die to surround the cavities and to have aperipheral line which does not extend outwardly from the partingsurface.

In the first aspect of the present invention, the second molding die mayhave a projection which extends outwardly from the parting surface sothat the projection is in contact with the O-ring when the first andsecond molding dies are clamped to each other. In one case, the firstmolding die may have a groove in which the O-ring is completelycontained, and the projection of the second molding die may have an endwhich goes into the groove to be in contact with the O-ring when thefirst and second molding dies are clamped to each other. In anothercase, the first molding die may have a groove in which the O-ring issupported, the O-ring partially being exposed from the groove toward thesecond molding die, and the projection may have an end which is widerthan the groove so that an outer surface of the projection is in contactwith the exposed portion of the O-ring when the first and second moldingdies are clamped to each other. In still another case, the first moldingdie may have a side with a groove in which the O-ring is supported, andthe projection may have an inner side which is in contact with theO-ring when the first and second molding dies are clamped to each other.

(2) Second Aspect of the Present Invention

According to a second aspect of the present invention, a molding die setincludes a molding die which comprises cavities, ejector holes each ofwhich extends to the corresponding cavity; ejector pins each of which ismovably arranged inside the corresponding ejector hole; and sealingmembers each of which air-seals the corresponding ejector hole.

In the second aspect of the present invention, the sealing members maybe O-rings each of which is arranged to surround the correspondingejector pin. In one case, the molding die set may further include acavity block comprising the cavities; and a cavity holder supporting thecavity block. Each of the ejector holes is formed through the cavityblock and cavity holder to have a wider diameter portion in which theO-ring is set. Each of the ejector pins may have a flange which is incontact with the corresponding O-ring to improve air sealing function.

(3) Third Aspect of the Present Invention

According to a third aspect of the present invention, a molding die setincludes a molding die which comprises cavities, pressure reducing pathsformed around the cavities; and a plurality of pressure reducing portsconnected to the pressure reducing paths, each of the pressure reducingports being arranged so as to minimize the distance from the farthestcavity.

In the third aspect of the present invention, the cavities may bearranged on two parallel lines in each of the first and second moldingdies, the pressure reducing paths are arranged at the both sides of thelines of cavities, and the pressure reducing ports are arranged at leastat the center of each of the pressure reducing paths.

A semiconductor device package according to the present invention isfabricated using one of the above described molding die sets of thefirst to third aspects of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cross-sectional view illustrating a conventionalmolding die set.

FIG. 2 is a partially cross-sectional view illustrating a molding dieset according to a first preferred embodiment of the present invention.

FIG. 3A is a cross-sectional view showing a part of the molding die set,shown in FIG. 2, in which parting surfaces are cleaned.

FIG. 3B is a cross-sectional showing a part of the molding die set,shown in FIG. 2, in which upper and lower molding dies are clamped toeach other.

FIG. 4 is a partially cross-sectional view illustrating a molding dieset according to a second preferred embodiment of the present invention.

FIG. 5 is a cross-sectional views showing a part of the molding die set,shown in FIG. 4.

FIG. 6 is a partially cross-sectional view illustrating a molding dieset according to a third preferred embodiment of the present invention.

FIG. 7 is a cross-sectional views showing a part of the molding die set,shown in FIG. 6.

FIG. 8 is a partially cross-sectional view illustrating a molding dieset according to a fourth preferred embodiment of the present invention.

FIG. 9 is a cross-sectional views showing a part of the molding die set,shown in FIG. 8.

FIG. 10 is a cross-sectional views showing a part of a molding die setaccording to a fifth preferred embodiment of the present invention.

FIG. 11 is a plan view illustrating an upper molding die of a moldingdie set according to a sixth preferred embodiment of the presentinvention.

FIG. 12 is a cross-sectional view showing the upper molding die, shownin FIG. 11.

DETAILED DISCLOSURE OF THE INVENTION

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings which form a part hereof,and in which is shown by way of illustration specific preferredembodiments in which the inventions may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention, and it is to be understood that otherembodiments may be utilized and that logical, mechanical and electricalchanges may be made without departing from the spirit and scope of thepresent inventions. The following detailed description is, therefore,not to be taken in a limiting sense, and scope of the present inventionsis defined only by the appended claims.

For better understanding of the present invention, a conventionaltechnology is first described. FIG. 1 shows a conventional molding dieset, in which the right half is only shown in sectional view. Theconventional molding die set includes a upper molding die 1 and a lowermolding die 2. The upper molding die 1 includes a mold chase unitcomposed of a cull block 11, cavity block 12 and a cavity holder 13. Thecull block 11 is arranged at the center of the upper molding die 1. Thecavity block 12 is arranged at the both sides of the cull block 11, andis supported by the cavity holder 13.

The mold chase unit (11, 12 and 13) is supported by ejector plates 14and support pins 15. The cull block 11 is provided with a cull 17. Thecavity block 12 has a plurality of cavities 18. The upper molding die 1further includes ejector pins 16 each of which extends through thecavity holder 13 and cavity block 12 for each cavity 18. The ejectorpins 16 are used when molded products are unloaded from the molding dieset. The upper molding die 1 still further includes an O-ring 19surrounding cavities 18 to air-seal and provide a pressure-reducedstructure.

The lower molding die 2 includes a mold chase unit composed of a potblock 21, cavity block 22 and a cavity holder 23. The pot block 21 isarranged at the center of the lower molding die 2. The cavity block 22is arranged at the both sides of the pot block 21, and is supported bythe cavity holder 23. The pot block 21 has a pot 27 therein.

The mold chase unit (21, 22 and 23) is supported by ejector plates 24and support pins 25. The cull block 21 is provided with a cull 27. Thecavity block 22 has a plurality of cavities 28. The lower molding die 2further includes ejector pins 26 each of which extends through thecavity holder 23 and cavity block 22 for each cavity 28. The ejectorpins 26 are used when molded products are unloaded from the molding dieset.

In operation, when the upper and lower molding dies 1 and 2 are clampedto each other, the O-ring 19 of the upper molding die 1 is in contactwith a parting surface of the lower molding die 2, so that the moldchase units are air-sealed to provide a pressure-reduced or vacuumedcondition.

According to the above described conventional molding die set, however,the pressured-reduced structure in the mold chases, especially in thecavities 18, may not work good enough. The following may be the reasons:

(1) When the surface of the molding dies are cleaned with a brush aftera resin mold process, the brush scrubs the O-ring too. As a result, theO-ring is worn away and broken; and therefore, an air leakage is made.

(2) Air leaks from around the ejector pins, so that it is difficult tomaintain the appropriate pressure in the cavities.

(3) The conventional molding die set includes a pressure-reduction portfrom which a vacuum is drawn, and a run off of bearing stress. It isdifficult to control the internal pressure of the plural cavitiesequally or in good balance.

First Preferred Embodiment

FIG. 2 shows a molding die set according to a first preferred embodimentof the present invention, in which the right half is only shown insectional view. The molding die set includes an upper molding die 101and a lower molding die 102. The upper molding die 101 includes a moldchase unit composed of a cull block 11, cavity block 31 and a cavityholder 13. The cull block 11 is arranged at the center of the uppermolding die 101. The cavity block 31 is arranged at both sides of thecull block 11, and is supported by the cavity holder 13.

The mold chase unit (11, 31 and 13) is supported by ejector plates 14and support pins 15. The cull block 11 is provided with a cull 17. Thecavity block 31 has a plurality of cavities 18. The upper molding die101 further includes ejector pins 16 each of which extends through thecavity holder 13 and cavity block 31 for each cavity 18. The ejectorpins 16 are used when molded products are unloaded from the molding dieset. The upper molding die 101 still further includes an O-ring 32provided at the bottom of the cavity block 31 to surround cavities 18and to air-seal and provide a pressure-reduced structure.

The lower molding die 102 includes a mold chase unit composed of a potblock 21, cavity block 37 and a cavity holder 23. The pot block 21 isarranged at center of the lower molding die 102. The cavity block 37 isarranged at both sides of the pot block 21, and is supported by thecavity holder 23. The pot block 21 has a pot 27 therein.

The mold chase unit (21, 37 and 23) is supported by ejector plates 24and support pins 25. The cull block 21 is provided with a cull 27. Thecavity block 37 has a plurality of cavities 28. The lower molding die102 further includes ejector pins 26 each of which extends through thecavity holder 23 and cavity block 37 for each cavity 28. The ejectorpins 26 are used when molded products are unloaded from the molding dieset.

The O-ring 32 is supported in a groove 33 designed to be deep enough sothat a peripheral line or the lowest line of the O-ring 32 does notproject or stick out of a parting surface 34. In other words, the O-ring32 is inset or positioned inwardly from the parting surface 34. Thegroove 33 is designed to have a wide bottom and a narrow opening end.

On the other hand, the cavity block 37 of the lower molding die 102 isprovided with a projection 38 that is to be in contact with the O-ring32. The projection 38 is formed to project out of the parting surface 34so as to push up the O-ring 32 when the upper and lower molding dies 101and 102 are clamped to each other for molding operation.

In operation, when the upper and lower molding dies 101 and 102 areclamped to each other, the projection 38 of the lower molding die 102gets into the groove 33 and is in contact with the O-ring 32, as shownin FIG. 3B. As a result, the mold chase units are air-sealed to providepressure-reduced or vacuumed condition.

After a molding operation, the parting surfaces 34 of the upper andlower molding dies 101 and 102 are cleaned with a brush 36 of a cleaner35, as shown in FIG. 3A. According to the molding die set, the brush 36will never be in contact with the O-ring 32, because the O-ring 32 ispositioned completely inside the cavity block 31. As a result, the brush36 does not scrub the O-ring 32; and therefore, the O-ring 32 is notworn away and broken.

In the above described first preferred embodiment, the O-ring 32 isprovided on the upper molding die 101 while the projection 38 isprovided on the lower molding die 102; however, the O-ring andprojection can be provided on the lower and upper molding dies,respectively, in the opposite manner.

Second Preferred Embodiment

FIG. 4 shows a molding die set according to a second preferredembodiment of the present invention, in which the right half is onlyshown in sectional view. FIG. 5 shows a part of the molding die set,shown in FIG. 4. The molding die set includes an upper molding die 201and a lower molding die 202. The upper molding die 201 includes a moldchase unit composed of a cull block 11, cavity block 41 and a cavityholder 13. The cull block 11 is arranged at the center of the uppermolding die 201. The cavity block 41 is arranged at both sides of thecull block 11, and is supported by the cavity holder 13.

The mold chase unit (11, 41 and 13) is supported by ejector plates 14and support pins 15. The cull block 11 is provided with a cull 17. Thecavity block 41 has a plurality of cavities 18. The upper molding die201 further includes ejector pins 16 each of which extends through thecavity holder 13 and cavity block 41 for each cavity 18. The ejectorpins 16 are used when molded products are unloaded from the molding dieset. The upper molding die 201 still further includes an O-ring 43provided at the bottom of the cavity block 41 to surround cavities 18and to air-seal and provide pressure-reduced structure.

The lower molding die 202 includes a mold chase unit composed of a potblock 21, cavity block 44 and a cavity holder 23. The pot block 21 isarranged at the center of the lower molding die 202. The cavity block 44is arranged at the both sides of the pot block 21, and is supported bythe cavity holder 23. The pot block 21 has a pot 27 therein.

The mold chase unit (21, 44 and 23) is supported by ejector plates 24and support pins 25. The cull block 21 is provided with a cull 27. Thecavity block 44 has a plurality of cavities 28. The lower molding die202 further includes ejector pins 26 each of which extends through thecavity holder 23 and cavity block 44 for each cavity 28. The ejectorpins 26 are used when molded products are unloaded from the molding dieset.

The O-ring 43 is supported in a groove designed to be deep enough sothat a peripheral line or the lowest line of the O-ring 43 does notproject or stick out beyond a parting surface 42. In other words, theO-ring 43 is positioned inwardly from the parting surface 42. The grooveis designed to have a wide bottom and a narrow opening end.

On the other hand, the cavity block 44 of the lower molding die 202 isprovided with a projected region 45 that is to be in contact with theO-ring 43. The projected region 45 is formed to project out beyond theparting surface 42 to be in contact with the O-ring 43 when the upperand lower molding dies 201 and 202 are clamped to each other for amolding operation.

In operation, when the upper and lower molding dies 201 and 202 areclamped to each other, the projected region 45 of the lower molding die202 is in contact with the O-ring 43. As a result, the mold chase unitsare air-sealed to provide a pressure-reduced or vacuumed condition.

After a molding operation, the parting surfaces 42 of the upper andlower molding dies 201 and 202 are cleaned with a brush, such as shownin FIG. 3A. According to the molding die set, the brush will never be incontact with the O-ring 43, because the O-ring 43 is positioned inwardlyfrom the parting surface 42. As a result, the brush does not scrub theO-ring 43; and therefore, the O-ring 43 is not worn away and broken.

In the above described second preferred embodiment, the O-ring 43 isprovided on the upper molding die 201 while the projected region 45 isprovided on the lower molding die 202; however, the O-ring and projectedregion can be provided on the lower and upper molding dies,respectively, in the opposite manner.

Third Preferred Embodiment

FIG. 6 shows a molding die set according to a third preferred embodimentof the present invention, in which the right half is only shown insectional view. FIG. 7 shows a part of the molding die set, shown inFIG. 6. The molding die set includes an upper molding die 301 and alower molding die 302. The upper molding die 301 includes a mold chaseunit composed of a cull block 11, cavity block 51 and a cavity holder13. The cull block 11 is arranged at the center of the upper molding die301. The cavity block 51 is arranged at the both sides of the cull block11, and is supported by the cavity holder 13.

The mold chase unit (11, 51 and 13) is supported by ejector plates 14and support pins 15. The cull block 11 is provided with a cull 17. Thecavity block 51 has a plurality of cavities 18. The upper molding die301 further includes ejector pins 16 each of which extends through thecavity holder 13 and cavity block 51 for each cavity 18. The ejectorpins 16 are used when molded products are unloaded from the molding dieset. The upper molding die 301 still further includes an O-ring 53provided at a side of the cavity block 51 to surround cavities 18 and toair-seal and provide a pressure reduced structure.

The lower molding die 302 includes a mold chase unit composed of a potblock 21, cavity block 54 and a cavity holder 23. The pot block 21 isarranged at the center of the lower molding die 302. The cavity block 54is arranged at the both sides of the pot block 21, and is supported bythe cavity holder 23. The pot block 21 has a pot 27 therein.

The mold chase unit (21, 54 and 23) is supported by ejector plates 24and support pins 25. The cull block 21 is provided with a cull 27. Thecavity block 54 has a plurality of cavities 28. The lower molding die302 further includes ejector pins 26 each of which extends through thecavity holder 23 and cavity block 54 for each cavity 28. The ejectorpins 26 are used when molded products are unloaded from the molding dieset.

The O-ring 53 is supported in a groove designed so that a peripheralline thereof does not project or stick out of a parting surface 52. Inother words, the O-ring 53 is positioned inwardly from the partingsurface 52. The groove for the O-ring 53 is designed to have a widebottom and a narrow opening end.

On the other hand, the cavity block 54 of the lower molding die 302 isprovided with a projected member 55 that is to be in contact with theO-ring 53. The projected member 55 is formed to project out of theparting surface 52 to be in contact at the inner side surface with theO-ring 53 when the upper and lower molding dies 301 and 302 are clampedto each other for molding operation.

In operation, when the upper and lower molding dies 301 and 302 areclamped to each other, the projected member 55 of the lower molding die302 is in contact at the inner side surface with the O-ring 53. As aresult, the mold chase units are air-sealed to provide pressure-reducedor vacuumed condition.

After a molding operation, the parting surfaces 52 of the upper andlower molding dies 301 and 302 are cleaned with a brush, such as shownin FIG. 3A. According to the molding die set, the brush will never be incontact with the O-ring 53, because the O-ring 53 is positioned inwardfrom the parting surface 52. As a result, the brush does not scrub theO-ring 53; and therefore, the O-ring 53 is not worn away and broken.

In the above described third preferred embodiment, the O-ring 53 isprovided on the upper molding die 301 while the projected member 55 isprovided on the lower molding die 302; however, the O-ring and projectedregion can be provided on the lower and upper molding dies,respectively, in the opposite manner.

Fourth Preferred Embodiment

FIG. 8 shows a molding die set according to a fourth preferredembodiment of the present invention, in which the right half is onlyshown in sectional view. The molding die set includes an upper moldingdie 401 and a lower molding die 402. The upper molding die 401 includesa mold chase unit composed of a cull block 11, cavity block 62 a and acavity holder 63 a. The cull block 11 is arranged at the center of theupper molding die 401. The cavity block 62 a is arranged at the bothsides of the cull block 11, and is supported by the cavity holder 63 a.

The mold chase unit (11, 62 a and 63 a) is supported by ejector plates65 a and support pins 15. The cull block 11 is provided with a cull 17.The cavity block 62 a has a plurality of cavities 61 a. The uppermolding die 401 further includes ejector pins 66 a each of which extendsthrough the cavity holder 63 a and cavity block 62 a for each cavity 61a. The ejector pins 66 a are used when molded products are unloaded fromthe molding die set. The upper molding die 401 still further includes anO-ring 32 provided at the bottom of the cavity block 62 a to surroundcavities 61 a and to air-seal and provide a pressure-reduced structure.

The lower molding die 402 includes a mold chase unit composed of a potblock 21, cavity block 62 b and a cavity holder 63 b. The pot block 21is arranged at the center of the lower molding die 402. The cavity block62 b is arranged at the both sides of the pot block 21, and is supportedby the cavity holder 63 b. The pot block 21 has a pot 27 therein.

The mold chase unit (21, 62 b and 63 b) is supported by ejector plates65 b and support pins 25. The cull block 21 is provided with a cull 27.The cavity block 62 b has a plurality of cavities 61 b. The lowermolding die 402 further includes ejector pins 66 b each of which extendsthrough the cavity holder 63 b and cavity block 62 b for each cavity 61b. The ejector pins 66 b are used when molded products are unloaded fromthe molding die set.

The O-ring 32 is supported in a groove 33 designed to be deep enough sothat a peripheral line or the lowest line of the O-ring 32 is notexposed or stick out of a parting surface 34. In other words, the O-ring32 is positioned inwardly from the parting surface 34. The groove 33 isdesigned to have a wide bottom and a narrow opening end.

On the other hand, the cavity block 62 b of the lower molding die 402 isprovided with a projection 38 that is to be in contact with the O-ring32. The projection 38 is formed to project out of the parting surface 34so as to get into the groove 33 and be in contact with the O-ring 32when the upper and lower molding dies 401 and 402 are clamped to eachother for molding operation.

FIG. 9 shows a part of the lower molding die 402 around the ejector pin66 b. The molding die set further includes ejectors 64 a and 64 bconnected to one end of the ejector pins 66 a and 66 b in the ejectorplates 65 a and 65 b, respectively. The ejector pins 66 a and 66 b aremovably extended in ejector holes 69 a and 69 b formed through thecavity holders 63 a and 63 b, and cavity blocks 62 a and 62 b,respectively. The ejector pins 66 a and 66 b pass through thecorresponding cavity (61 a and 61 b). In FIG. 9, the ejector pin 66 b ispositioned in the cavity block during a molding process, and then, theejector pin 66 b is moved up when molded products are unloaded after themolding process.

The cavity holders 63 a and 63 b are provided with grooves 68 a and 68 bin which O-rings 67 a and 67 b are supported, respectively. The groovescan be formed in the cavity blocks 62 a and 62 b.

In operation, when the upper and lower molding dies 401 and 402 areclamped to each other, the projection 38 of the lower molding die 402gets into the groove 33 and is in contact with the O-ring 32, in thesame manner as shown in FIG. 3B. As a result, the mold chase units areair-sealed to provide pressure-reduced or vacuumed condition.

Further, according to the fourth preferred embodiment, an air-leak isnot generated around the ejector pins 66 a and 66 b, so that thepressure in the cavities can be kept at an appropriate level.

Fifth Preferred Embodiment

FIG. 10 shows a part of a lower molding die of a molding die setaccording a fifth preferred embodiment of the present invention. Sincethe fifth preferred embodiment is similar to the above-described fourthpreferred embodiment, only the differences between them are described indetail to avoid redundant description. The lower molding die includes anejector pin 72 having a flange 73 to be in contact with an O-ring 75supported in a groove 74. The ejector pin 72 is sealed by the O-ring 75between the flange 73 and the cavity holder 63. This type of sealingmechanism can be called “vertical sealing” relative to “horizontalsealing” for the fourth preferred embodiment, shown in FIG. 9.

The ejector pin 72 is positioned under the cavity block 62 during amolding process, and then, the ejector pin 72 is moved up when moldedproducts are unloaded after the molding process.

According to the fifth preferred embodiment, the same or similaradvantages to the fourth preferred embodiment can be obtained.

Sixth Preferred Embodiment

FIG. 11 is a plan view illustrating an upper molding die of a moldingdie set according to a sixth preferred embodiment of the presentinvention. FIG. 12 is a cross sectional view showing the upper moldingdie, shown in FIG. 11. The upper molding die includes a cull block 82having culls 81; a cavity block 84 having cavities 83; and a cavityholder 85 supporting the cull block 82 and cavity block 84. The cullblock 82 is arranged around the center of the cavity holder 85, whilethe cavity block 84 is arranged at both side of the cull block 82.

The cavity block 84 is provided with an O-ring 86 for air-seal. On thecavity block 84, surface pressure paths 87 are formed inside of theO-ring 86 to allow surface pressure escapes outwardly. The cavity block84 has a pair of pressure reducing grooves 89, arranged inside thesurface pressure paths 87. The pressure reducing grooves 89 areconnected to pressure reducing ports 88, which are arranged at thecenter of the pressure reducing grooves 89 in the up-down direction inFIG. 11. The pressure reducing grooves (paths) 89 may be designed tohave a depth of between 0.1 mm to 10 mm. Although, in this embodiment,the pressure reducing grooves 89 are arranged at both sides of thecavity lines, four regions of pressure reducing grooves can be providedto surround all the cavities 83.

The cavity block 84 is provided with a pass-through hole connected tothe pressure reducing ports 88 so that air in the cavities 83 are drawnthrough them. According to the sixth preferred embodiment, the pressurereducing ports 88 are positioned in good balance. In other words, eachof the pressure reducing ports 88 is positioned so as to minimize thedistance from the farthest cavity. Although, in this embodiment, twopressure reducing ports are provided, more ports can be formed on thecavity block.

According to the sixth preferred embodiment, the pressure reducinggrooves 89 are formed around the cavities 83 and the pressure reducingports 88 are arranged in good balance, so it is easy to keep thecavities 83 at a desired pressure level.

The sixth preferred embodiment is applicable to a lower molding die.

The above-described first to sixth preferred embodiments can be combinedin any manners. According to the present invention, it can be reducedthe amount of voids conventionally generated in resin-molded IC and LSIchips.

What is claimed is:
 1. A molding die set, comprising: a first moldingdie which comprises first cavities and a first parting surface, thefirst parting surface surrounding the first cavities to define the firstcavities; a second molding die positioned outwardly relative to thefirst molding die and which comprises second cavities and a secondparting surface arranged to face the first molding die, the secondparting surface surrounding the second cavities to define the secondcavities, the second parting surface being in contact with the firstparting surface during a molding operation, the second parting surfacebeing separated from the first parting surface after the moldingoperation; and an O-ring supported on the first molding die to surroundthe first cavities, the O-ring being engaged with the second molding dieduring the molding operation to seal the first and second cavities, theO-ring being positioned completely inwardly relative to the firstparting surface both during and after the molding operation, therebyallowing the first parting surface to be cleaned after the moldingoperation without touching the O-ring.
 2. A molding die set according toclaim 1, wherein the second molding die has a projection which extendsoutwardly from the second parting surface so that the projection is incontact with the O-ring when the first and second molding dies areclamped to each other.
 3. A molding die set according to claim 2,wherein the first molding die has a groove in which the O-ring iscompletely contained, and the projection of the second molding die hasan end which goes into the groove to be in contact with the O-ring whenthe first and second molding dies are clamped to each other.
 4. Amolding die set according to claim 3, wherein the groove has a bottomand an opening which is narrower than the bottom so that the O-ring issupported securely therein.
 5. A molding die set according to claim 2,wherein the first molding die has a groove in which the O-ring issupported, the O-ring partially being exposed from the groove toward thesecond molding die, and the projection has an end which is wider thanthe groove so that an outer surface of the projection is in contact withthe exposed portion of the O-ring when the first and second molding diesare clamped to each other.
 6. A molding die set according to claim 2,wherein the first molding die has a side with a groove in which theO-ring is supported, and the projection has an inner side which is incontact with the O-ring when the first and second molding dies areclamped to each other.
 7. A molding die set according to claim 1,wherein each of the first and second molding dies has ejector holes eachof which extends to the corresponding cavity; ejector pins each of whichis movably arranged inside the corresponding ejector hole; and sealingmembers each of which air-seals the corresponding ejector hole.
 8. Amolding die set according to claim 7, wherein the sealing members areO-rings each of which is arranged to surround the corresponding ejectorpin.
 9. A molding die set according to claim 8, further comprising: acavity block comprising the cavities; and a cavity holder supporting thecavity block, wherein each of the ejector holes is formed through thecavity block and cavity holder to have a wider diameter portion in whichthe O-ring is set.
 10. A molding die set, comprising: a first moldingdie which has a cavity block that includes cavities, a cavity holderthat supports the cavity block, and a parting surface; a second moldingdie which has a cavity block that includes cavities, a cavity holderthat supports the cavity block, and a parting surface arranged to facethe first molding die; and an O-ring supported on the first molding dieto surround the cavities and to have a peripheral line which does notextend outwardly from the parting surface; wherein each of the first andsecond molding dies has ejector holes each of which extends to thecorresponding cavity; ejector pins each of which is movably arrangedinside the corresponding ejector hole; and sealing members each of whichairseals the corresponding ejector hole; wherein the sealing members areO-rings each of which is arranged to surround the corresponding ejectorpin; wherein each of the ejector holes is formed through the cavityblock and cavity holder to have a wider diameter portion in which theO-ring is set; and wherein each of the ejector pins has a flange whichis in contact with the corresponding O-ring to improve air sealingfunction.
 11. A molding die set according to claim 1, wherein one of thefirst and second molding dies comprises pressure reducing paths formedaround the cavities; and a plurality of pressure reducing portsconnected to the pressure reducing paths, each of the pressure reducingports being arranged so as to minimize the distance from the farthestcavity.
 12. A molding die set according to claim 11, wherein thecavities are arranged on two parallel lines in each of the first andsecond molding dies, the pressure reducing paths are arranged at theboth sides of the lines of cavities, and the pressure reducing ports arearranged at least at the center of each of the pressure reducing paths.13. A molding die set, comprising: a molding die which comprisescavities and a first parting surface that surrounds and defines thecavities, an O-ring that provides a seal between the first partingsurface and a second parting surface of a further molding die during amolding operation and that is positioned completely inwardly relative tothe first parting surface both during and after the molding operation soas to allow the first parting surface to be cleaned after the moldingoperation without touching the O-ring, the second parting surface beingpositioned outwardly relative to the first parting surface, ejectorholes each of which extends to the corresponding cavity; ejector pinseach of which is movably arranged inside the corresponding ejector hole;and sealing members each of which air-seals the corresponding ejectorhole.
 14. A molding die set according to claim 13, wherein the sealingmembers are O-rings each of which is arranged to surround thecorresponding ejector pin.
 15. A molding die set according to claim 14,further comprising: a cavity block comprising the cavities; and a cavityholder supporting the cavity block, wherein each of the ejector holes isformed through the cavity block and cavity holder to have a widerdiameter portion in which the O-ring is set.
 16. A molding die set,comprising: a molding die which comprises a cavity block that hascavities, a cavity holder supporting the cavity block, ejector holeseach of which extends to the corresponding cavity; ejector pins each ofwhich is movably arranged inside the corresponding ejector hole; andsealing members each of which air-seals the corresponding ejector hole;wherein the sealing members are O-rings each of which is arranged tosurround the corresponding ejector pin; wherein each of the ejectorholes is formed through the cavity block and cavity holder to have awider diameter portion in which the O-ring is set; and wherein each ofthe ejector pins has a flange which is in contact with the correspondingO-ring to improve air sealing function.
 17. A molding die set accordingto claim 13, wherein the molding die comprises pressure reducing pathsformed around the cavities; and a plurality of pressure reducing portsconnected to the pressure reducing paths, each of the pressure reducingports being arranged so as to minimize the distance from the farthestcavity.
 18. A molding die set according to claim 17, wherein the moldingdie is a first molding die; wherein the further molding die is a secondmolding die; and wherein the cavities are arranged on two parallel linesin each of the first and second molding dies, the pressure reducingpaths are arranged at the both sides of the lines of cavities, and thepressure reducing ports are arranged at least at the center of each ofthe pressure reducing paths.
 19. A molding die set, comprising: amolding die which comprises cavities and a first parting surface thatsurrounds and defines the cavities, an O-ring that provides a sealbetween the first parting surface and a second parting surface of afurther molding die during a molding operation and that is positionedcompletely inwardly relative to the first parting surface both duringand after the molding operation so as to allow the first parting surfaceto be cleaned after the molding operation without touching the O-ring,the second parting surface being positioned outwardly relative to thefirst parting surface, pressure reducing paths formed around thecavities; and a plurality of pressure reducing ports connected to thepressure reducing paths, each of the pressure reducing ports beingarranged so as to minimize the distance from the farthest cavity.
 20. Amolding die set according to claim 19, wherein the molding die is afirst molding die, and the further molding die is a second molding die,and wherein the cavities are arranged on two parallel lines in each ofthe first and second molding dies, the pressure reducing paths arearranged at the both sides of the lines of cavities, and the pressurereducing ports are arranged at least at the center of each of thepressure reducing paths.